The beneficial effect of zinc compounds in dental compositions, especially in toothpastes and mouthwashes, has been generally recognized for some time. In U.S. Pat. No. 4,100,269, issued July 11, 1978 to Morton Pader, there is disclosed the use of insoluble zinc compounds in dentifrices for improving the control of calculus. Insoluble zinc compounds employed in the patent are those having a solubility of less than about one gram of zinc per 100 cc of water at 20.degree. C. and preferably a solubility of not more than about 0.5 gram zinc compound per 100 cc water at 20.degree. C. Among the typical insoluble zinc compounds employed in the patent is zinc citrate. Zinc acetate and hydroxide have been recognized as having anti-plaque properties in dentifrices as disclosed in Hanke, M. T., J. Amer. Dental Assoc., 27(9), 1379-93 (1940). The pyrophosphate, tetrametaphosphate, metaphosphate and orthophosphate salts of zinc have been known to be effective in tartar removal as disclosed in W. German Patent Specification No. 1,251,468, assigned to Chemische Fabrik Budenheim and published Oct. 5, 1967. Also it has been known to formulate tooth powders containing zinc citrate and calcium gluconate such as disclosed in U.S. Pat. No. 1,861,189 issued May 31, 1932 to Charles Pfizer.
In addition, zinc chloride has been used in mouthwash compositions and recognized as possessing anti-mouth odor properties in said compositions.
However, despite the heretofore known use of zinc compounds in dental compositions their use has not been without certain undesirable drawbacks and side-effects. For example, when such zinc compounds have been employed it has not been possible to satisfactorily include ionic fluoride in the compositions due to the chemical incompatibility therebetween. Moreover, while zinc chloride possesses the desired anti-odor activity, its high level of astringency is undesirable. Yet other zinc compounds, such as for example, zinc citrate are so slightly soluble in aqueous solutions that while the level of astringency is kept acceptably low, there is an undesirable loss in anti-mouth odor activity of the zinc compound.
It is therefore highly desirable to provide a zinc derivative that is less astringent than zinc chloride so as to provide enhanced acceptance by users of dental compositions containing same yet without sacrificing anti-odor activity. It is also desirable to provide a zinc derivative having higher aqueous solubility than zinc citrate yet not as astringent as zinc chloride. Additionally it is desirable to provide a zinc derivative of said properties that does not present substantially any chemical incompatibility problem in dental compositions employing an ionic fluoride salt.